Interventional radiology procedures are becoming more prevalent for the detection and treatment of many diseases and injuries. Often an interventional radiology procedure involves the viewing of a catheter, or needle, as it is directed into a desired position within the body. Catheter based medical procedures are commonplace and include such medical treatments as balloon angioplasty, laser ablation, the installation of stints and many other valuable treatments. In such medical procedures the progress of the catheter is typically monitored, within a patient's body, by an X-ray fluoroscope imaging system.
During a catheterization procedure, physicians and technicians need to position themselves next to the patient, in order to control the catheter. The overall X-ray exposure to such medical personnel can be higher than the X-ray exposure to the patient because medical personnel may do several X-ray fluoroscopic procedures in a single day and receive multiple dosages of X-ray radiation. For example, neuroangiographic procedures to repair an aneurysm or malformation may take as long as ten hours, during which the patient and physician are exposed to X-ray radiation much of the time. If the physician performs several such procedures a year, the physician quickly may exceed the recommended maximum dosage of radiation. The results of this potential for overexposure has been for highly trained physicians and other technical medical personnel to reduce their work load or to not wear their radiation monitor. Similarly, concern over overexposure may cause a physician to hurry a procedure, thus increasing the chances of making a mistake.
One way to reduce X-ray exposure from fluoroscopy is to use various shielding techniques. Staff can be protected with lead aprons, imaging chain canopies, lead gloves, and eye shields. Patients can be protected with gonad shields, etc. Many of these techniques are not often used because they interfere with the clinical procedure in one way or another.
In X-ray fluoroscopy it is well known that the dosage of the X-ray radiation is inversely proportional to the quantum noise in the viewed image. Prior art methods of X-ray dose reduction have addressed lowering the rate of dosage. For example, a nominal operational rate for X-ray fluoroscope is 30 frames/sec which may result in an exposure of approximately 10R/min skin dose. Prior art methods have attempted to reduce exposure by reducing the operational rate, for example, from 30 frames/sec. to 15 frames/sec. Such techniques have not been successful since a reduced frame rate necessitates an increased dosage rate per frame to minimize the quantum noise, the net result being no significant reduction in exposure.
Other techniques for reducing the dosage of X-ray radiation include operating the fluoroscopy imaging system in a zoom mode; in other words, limiting the X-ray radiation to a small region and electronically magnifying that region to form the entire viewed image Zoom mode imagery is not popular among some medical personnel because the zoomed image only permits a physician to view a small segment of a patient's body. Such a limited view makes it difficult for a physician to orient the placement of a catheter in a body, and prevents a physician from anticipating upcoming obstacles in the body until they appear in the zoomed image. In addition, in zoom mode, some X-ray systems increase the X-ray tube output dose such as to maintain a constant level of light output from the image intensifier. In that case, there is no dose saving to the patient.
It is therefore desirable to provide an apparatus and method for reducing X-ray radiation exposure to both patients and medical personnel without adversely affecting either the area of interest the X-ray fluoroscope procedure is being used to view, or the physician's ability to view the peripheral regions surrounding the area of interest.
Apparatus and a method for reducing the dosage of X-ray radiation incurred by a patient and medical personnel during a fluoroscopic procedure are disclosed in applicant's copending applications entitled APPARATUS AND METHOD FOR REDUCING X-RAY DOSAGE DURING A FLUOROSCOPIC PROCEDURE and METHOD FOR TRACKING A CATHETER PROBE DURING A FLUOROSCOPIC PROCEDURE, filed concurrently herewith and whereof the disclosures are herein incorporated by reference. During a fluoroscopic procedure X-rays are passed through a patient and are converted into a viewed image. Traditionally, the input X-ray beam is unattenuated across the entire field of view, even though it is herein recognized that, with some procedures, only a small area of the field of view actually requires high definition imaging The present invention includes a filter member that attenuates the X-ray radiation in areas of the field of view that are not of primary interest. With the filter member in place, a physician can still visualize the entire field of view for the purposes of orientation and placement, except that now the areas in the viewed image outside the point of interest are of lower quality. By attenuating the X-ray radiation in the areas outside the point of interest, the integrated-area dosage of X-rays is greatly reduced, as is the chance of overexposure to either the patient or the physician. There is an analogy to the retina fovea mechanism of the human eye to track an object of interest. Thus the concept is also referred to herein as an "X-ray fovea".
The attenuation of the X-ray radiation in selective areas changes in the brightness of the viewed image. Thus, the areas of the viewed image created by the attenuated X-rays are amplified to match the brightness of the viewed image created by the unattenuated X-rays. To prevent a distinct division of the viewed image between the areas formed by the attenuated and unattenuated X-rays, special image processing algorithms must be used. In addition, the filter member can have a varying transparency to X-rays, such that a smooth transition is made between the various regions of the viewed image and no discernable transition line appears in the image. In addition to compensating the brightness in the peripheral area, one may also introduce temporal or spatial filtering to reduce noise.
In one arrangement, the filter member is a substantially planar structure having a single aperture formed therethrough, the planar structure decreasing in thickness in the transition area such that the thickness of the planar structure is at a minimum at the edge of the aperture. Images of the filter plate or fovea collimator are obtained and algorithms on a workstation then find the center of the filter plate hole. Although the size of the filter plate hole changes with geometric magnification, the center remains fixed. Compensation of the image with regard to intensity and magnification changes requires finding the filter plate edge. Localization of the filter plate is also required for positioning the filter plate over an area of interest automatically by a systems controller.